Macromolecules 1984,17, 134-138
134
Science Foundation under Grant No. 78-11955. Registry No. I, 88392-12-5;11, 88392-13-6;X, 88392-14-7;i, 6289-83-4; iii, 35236-42-1; (trans-l,4-cyclohexanediol)~(trans1,4-cyclohexanedicarbonylchloride) (copolymer), 88392-15-8; poly(oxy-trans-1,4-cyclohexyleneoxycarbonyl-trans-l,4-~yclo-
References and Notes (1) Polk, M. B.; Bota, K. B.; Akubuiro, E. C.; Phingbodhipakkiya, M. Macromolecules 1981, 14, 1626. (2) Doering, W. E.; Farber, M.; Sayigh, A. J. Am. Chem. SOC. 1952, 74, 4370. (3) Oberg, R. C.; Pines, H.; Ipatieff, V. N. J.Am. Chem. SOC. 1944, 66, 1096. (4) Sadtler Standard13C NMR Spectra;SadtlerResearch Laboratories: Philadelphia, 1976. (5) Polk, M. B.; Bota, K. B.; Akubuiro, E. C. Ind. Eng. Chem. Prod. Res. Dev. 1982,21, 154. (6) Stothers, J. B. "Carbon-13 NMR Spectroscopy"; Academic Press: New York, 1972.
hexylenecarbonyl), 88392-1@3; (2-methylresorcino1)'(terePh~oY1
chloride) (copolymer), 88392-16-9; poly(oxy-2-methyl-l,3phenyleneoxyterephthaloyl), 88392-11-4; (cis-1,4-cyclohexanediol)~(trans-l,4-cyclohexanedicarbonylchloride) (copolymer),88392-17-0;poly(oxy-cis,trans-l,4-cyclohexyleneoxycarbonyl-trans-l,4-cyclohexylenecarbonyl), 88424-59-3.
Hydrolysis Polymerization of Spiro(acy1pentaoxy)phosphoranes to Polyphosphates Shiro Kobayashi, Yukitoshi Narukawa, and Takeo Saegusa* Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan. Received March 24, 1983 ABSTRACT: Reaction of spiro(acy1pentaoxy)phosphoranes la-c induced by an 0-nucleophileof water gave polyphosphate 2 made of phosphate diester unit 2a and phosphate triester unit 2b ('hydrolysis polymerization" of 1). The content of 2a and 2b was determined by two methods: the 31PNMR method on the benzoylated polymer and the IR method on the polymer salts with triethylamine. The mechanism of the hydrolysis polymerization is outlined as follows. The reaction of 1 with water rapidly forms acyclic and cyclic phoshate triester intermediates (7and 8,respectively). 7 and 8 are still reactive, and subsequent reactions between these species slowly take place to yield polyphosphate 2 via two modes of reaction: a polycondensation and a ring-opening addition polymerization. Our recent investigations have disclosed that spiro(acy1oxy)phosphoranes are quite reactive pentacovalent phosphorus species and can be used as starting monomers to give various phosphorus-containing polymers,' e.g., polyphosphates,2-6 polyphosph~nates,~~' and polyphosphinates.66 All these polymerizations have been considered to proceed via phosphonium zwitterion intermediates.' During the course of these studies we have found that spiro(acy1oxy)phosphoranes are good amphiphiles; they react with both nucleophiles and electrop h i l e ~ . ~Recently, J~ we reported the reaction of spiro(acy1pentaoxy)phosphoranes 1, containing a PhO group
lymerization of spiro(acy1pentaoxy)phosphoranes la-c induced by the reaction of 1 with an another 0-nucleophile of water, which gives rise to polyphosphate 2 containing both open-chain phosphate diester unit 2a and phosphate triester unit with pendant carboxylic acid group 2b ("hydrolysis polymerization"). The present water-induced polymerization (reaction 1) is unique from the standpoint that in ionic polymerization water is normally an undesirable impurity and hence should be removed from the reaction system. In contrast,
0 R' R O H I-PhOH) ( a l c o h o l yst5 polymerization I
LPR'
II
0
II W C H ~ C H ~ O PI O W I OCHCON~;
2a
la, R = Ph
0
(-PhOH)
(aminoiysis polymertiation)
0
I
OH
OR
PhO-PMo
R'R'NH
I1 I
~~CH~CH~OPOCHCO~VJ
b, R = CF,CH, c, R = CCl,CH,
f
0
II
wCH2CH20POw
I
1
OCHC02H
R
0 R'
II I I NM
Me
w C H ~ C H ~ O P 0 C H C O ~ ~
with alcohols acting as an 0-nucleophile to give polyphosphate triesters having alcohol components incorporated ("alcoholysis polymerization" of l).3 Polymerization of 1 has also been induced by the reaction of 1 with Nnucleophiles of amines and ammonia to give polyphosphate derivatives possessing the amine and ammonia components, respectively ("aminolysis and ammonolysis polymerizations")." The present paper describes the po-
(1)
2b
water is an indispensable component in the present polymerization and is incorporated into the polymer (2) with the liberation of an alcohol.
Results and Discussion Hydrolysis Polymerization of Spiro(acy1penta0xy)phosphorane1 Induced by Water. The polymerization of 1 with water was carried out at room temperature by using a stoichiometricor a small excess amount of water for 1. Solvents employed were acetonitrile, chloroform,
0024-929718412217-0134$01.50/0 0 1984 American Chemical Society
Macromolecules, Vol. 17,No. 2, 1984
Polymerization of Spiro(acy1pentaoxy)phosphoranes 135 Table I
Hydrolysis Polymerization of 1 entry no. 1
2 3 4 5 6 7 8
yield, %
R of 1
mmol of H*O
solvent
Ph Ph Ph Ph Ph Ph CF,CH, CCl,CH,
3.3 3.3 3.3 3.0 3.9 3.6 3.0 3.3
CH,CN CH,CN CH ,CN CH,CN CHCl, DMF CH,CN CH ,CN
[Phosphorane 11 = 3.0 mmol in 3 mL of solvent. in DMF at 55 "C.
temp rt rt rt 90 "C rt rt rt rt
0 Buo-p-oBu
I
OH
3 ("P NMR 6 -1.0)
X
pyrldlne
polymer
ROH
mol wtc
5 24 120 18 24 96 72 72
49 74 78 74 80 66 76 74
78 80 80 61 80 83 72 82
960 1500 2300 2300 1100 2000 1800 2000
rt = room temperature.
and DMF. In DMF solvent the reaction was homogeneous throughout the polymerization, whereas in acetonitrile or chloroform the reaction mixture formed two layers with the progress of the reaction. After the reaction, the mixture was poured into dry diethyl ether to precipitate polymeric materials. The polymer obtained was a viscous oil or powdery solid, depending on the molecular weight. The polymer was soluble in aprotic polar solvents such as DMF and Me2S0 and in protic solvents such as methanol, trifluoroethanol, and water. During the reaction, a hydroxyl compound, e.g., phenol in entry no. 1-6 of Table I, trifluoroethanol in no. 7, and trichloroethanol in no. 8, was liberated and the amount of the alcohol was determined by the GLC analysis of the diethyl ether layer. These results are given in Table I. Reaction 1 is a new polymerization of 1 induced by water and, hence, can be termed the "hydrolysis polymerization" of phosphorane 1. Polymer Structure. The IR spectrum of the polymer (no. 4, neat) showed characteristic absorptions at 3350 (br, 1740 (vm), and 1210 (br, y?po) cm-'. The 'H NMR spectrum of the polymer (M@O-d6, Me4Si)showed broad signals a t 6 1.2-1.6 (3.0 H, CH3), 3.7-4.4 (4.0 H, OCH2CH20),and 4.4-5.0 (1.0 H, OCH). In addition to these signals, a peak at 6 7.0-7.3 ascribable to phenyl protons (0.34 H) was observed, indicating the presence of phenoxy group in the polymer. The 31PNMR spectrum of the polymer (Me2SO-d6)showed a signal at 6 -2.2 (relative to 85% H3P04external standard). Anal. Calcd for (C5H906P),: C, 30.62; H, 4.63; P, 15.79. Found C, 30.88; H, 5.04; P, 15.66. All the above data indicate that the polymer is constructed from phosphate diester 2a, phosphate triester 2b, or both units. It is not possible from the above data to distinguish the unit structure of 2a and 2b. To determine the polymer structure in an unambiguous way, polymers were examined according to the following two methods. NMR Method. As mentioned above NMR signals of the phosphate diester and triester appear in the same region around -2 ppm. Therefore, the polymer was modified by a chemical reaction. It is known that a phosphate diester reacts with carboxylic acid chloride to give an acyl phosphate.12 First, a model reaction was carried out. Di-n-butyl phosphate (3) was subjected to P
time, h
BuO-P-OBu
I
OCPh
II
0
4 ('IP NMR 6 -8.4)
the reaction with benzoyl chloride in the presence of
Determined by vapor pressure osmometry
Table I1 Content of Units 2a and 2b in Polymer 2 sample polymer no.
31PNMR method
IR method
2a,
2b9
25 82 80 71 87 54 40 30
75 18 20 29 13 46 60 70
%
%
log
log (To/T)im 6a
(To/!Uiwo
0.02 0.13 0.1 2 0.11 0.15 0.09
0.10 0.09 0.04 0.04 0.07 0.08
6b
pyridine. Then di-n-butyl benzoyl phosphate (4) was quantitatively formed, which was confirmed by the complete disappearance of the NMR signal at 6 -1.0 due to 3 accompanied by the appearance of a new signal at 6 -8.4 due to 4. Under similar reaction conditions the 31PNMR signal of tri-n-butyl phosphate (-0.8 ppm) as a model of unit 2b remained unchanged. Therefore, the bemylation will not affect the phosphate triester moiety of unit 2b. The benzoylation of polymer 2 should give unit 5a from unit 2a. Indeed, 5a, the benzoylated unit, exhibited a 31P NMR signal at 6 -8.5. Under the bemylation conditions 0 Me
OCPh
II0
5a ( 31PNMR 6 -8.5)
of the polymer, the carboxylic acid group of unit 2b might partially be benzoylated to give carboxylic anhydride. However, the 31PNMR signal of such a compound still appeared at 6 -2.3, indicating that the chemical shift of unit 2b is not changed upon treatment with benzoyl chloride. Thus, the benzoylated polymer exhibited two 31PNMR signals, one at 6 -8.5 and another at -2.3, respectively. From the integration ratio of these signals the unit content of 2a and 2b could be determined. As shown in Table I1 all polymers consisted of both units. Polymer (sample no. 1) obtained with a shorter reaction time, e.g., 5 h, contained more triester unit 2b than diester unit 2a. With a longer reaction time or at a higher reaction temperature of 90 OC, 2a became a major unit. In the reaction in DMF, the content of 2a was almost comparable to the content of 2b. IR Method. The second way to obtain information on the polymer structure was IR spectroscopy, with special attention paid to the carbonyl stretching band. Acidic
Macromolecules, Vol. 17, No. 2, 1984
136 Kobayashi, Narukawa, and Saegusa
Nle
0 Me
/I I
OPh
9 ("P NMR 6 -6.9,-7.4)
/Y
II
T I
I
I
I
I
I
1740 1600 Cm-'
Figure 1. IR spectra of (a) polymer sample no. 6 and (b) polymer sample no. 6 and triethylamine; Toand T denote the transmittance at the point indicated in the figure.
hydrogens of both 2a and 2b protonate triethylamine to form salts 6a and 6b, respectively. With the addition of 0 Me
I1 I I
II I OCHCOi-Et3NH t
t
I
I
6a
Me
6b
triethylamine to the polymer solution, the v c d band of carboxylic acid ester unit 6a was not affected and appeared in the same region as 2a i.e., at 1740 cm-'. However the v m band of carboxylate anion 6b appeared at 1600 cm-' (Figure 1). Thus, the values of log (To/T)at 1740 and 1600 cm-' were obtained with a base-line method (Figure lb) and were taken as a measure of the content of units 2a and 2b, respectively (Table 11). These values of log (To/ T )are in accord with those obtained by the 31PNMR method, and these results strongly support the presence of both units 2a and 2b in the polymers obtained by the hydrolysis polymerization. Polymerization Mechanism. In order to shed light on the mechanism of hydrolysis polymerization, the early stage of the reaction of 1 with water was followed by 31P NMR spectroscopy. It was found that the reaction of l a with water (1:l molar) was very rapid; Le., the 31PNMR signals of l a (6 -39.0 and -39.3 ppm in acetonitrile) disappeared completely within 10 min at 0 "C, and new signals appeared at 6 -7.1 and -7.4 and at 6 +16.6. These two groups of signals were assigned respectively to an openchain phosphate triester 7 and a cyclic triester 8, both having a carboxylic group. The fractions of 7 and 8 were la
+
H20
-
10 ("P NMR
la
"20
A'LT I r\ /OB
H-0-Pfl
course A
/
IO ' Ph
course B
OCHC02H
I
-------
Me
a hexacoordinate intermediate.9 11 is a very unstable species and further causes ring opening to give 7 via course A or eliminates phenol to yield 8 via course B. 7 and 8 are unstable and still reactive. They were consumed slowly, and in turn polymer formation was observed by NMR. As mentioned above, the polymer obtained in a shorter reaction time contained unit 2b predominantly whereas the polymer obtained with longer reaction time contained 2a as the major unit. This result would suggest that unit 2b is formed at the early stage of polymerization and is isomerized later to unit 2a.13 Elucidation of this point, however, requires further studies. From all of these observatons the following reaction course is postulated. 7, first formed from la and water, possesses an alcoholic OH group. It is well-known that an alcohol induces a nucleophilic attack on the phosphorus atom of phosphate triesters such as 7 and 8.14 The alcoholic hydroxyl group of 7 attacks the phosphorus atom of another 7 to produce unit 12 with the elimination of phenol. The nucleophilic attack of the hydroxyl group of 7 also takes place on the phosphorus of 8, leading also to the formation of unit 12. Repetition of these reactions
PYH
7
HOCH2CH20PO-
t -PhOH
7 ("P NMR 6 -7.1, -7.4)
ie
0, /OCHC02H
lI
0
a +CH2CH2OPO*II 7 or 8
I
OCHC02H
OCHC02H
I
+PhOH
Me
Me
12
2b
/ 0
co/p\o
8 (31PNMR 6
8 t PhOH
11
0 Me
II I HOCH2CH20POCHC02H I OPh
6 t 17.0)
,-n+
MCH2CH20PO-
O-*Et )N H
,OCHCOzMe
dependently prepared, isolated, and characterized for the confirmation of the structure. The 31PNMR (CDC13) signals were as follows: 9; 6 -6.9 and -7.4; 10, 6 +17.0. These data were taken to support the structures of 7 and 8. Two peaks of 7 and 9 with equal intensity are due to the presence of two diastereomers arising from the asymmetric carbon atom of POCH(Me). Formation of 7 and 8 was explained in the following manner. A nucleophilic attack of water on the central phosphorus atom of la gives hydroxyphosphorane 11 via
0
mCH2CH2OPOCHCO2-
I
,0,
I1 I 1 OH Me
+ 16.6)
about 66% and 34%, respectively, at an early stage of reaction. Since 7 and 8 were very unstable under the reaction conditions, model compounds 9 and 10 were in-
tCHzCH20POCHC02
8
2a
+-
Macromolecules, Vol. 17,No. 2, 1984
Polymerization of Spiro(acy1pentaoxy)phosphoranes 137
of 7 or 8 with 12 will ultimately produce polymer 2b. It is also reasonable to envisage an interconversion between 7 and 8. If the proposed course is right, a phenoxy group could be present at the polymer end. This was actually confirmed by 'H NMR of polymer sample no. 4. On the assumption that one phenoxy group is present at the polymer end an attempt was made to calculate the degree of polymerization (DP) from the lH NMR data, leading to DP = 15 (molecular weight = 3000). This value is not inconsistent with the value of 2300 obtained by vapor pressure osmometry. The mode of polymerization of phenyl phosphate 7 with 12 is a polycondensation while that of cyclic phosphate 8 with 12 is a ring-opening addition polymerization. The intermediacy of hydroxyphosphorane 13 or hydroxyphosphonium zwitterion 14 from 8 is at present less likely.
8 -
unit
2a
I
Me
0
14
13
Experimental Section Materials. Spiro(acy1pentaoxy)phosphorane la was prepared according to our method from 2-phenoxy-l,3,2-dioxaphospholane and pyruvic acid.16 l b was obtained by the reaction of 2-(2,2,2trifluoroethoxy)-1,3,2-dioxaphospholane with pyruvic acid: 31P NMR (CDC13) 6 -38.2, -38.7; 'H NMR (CDCl3) 6 1.45 (d, J = 7 Hz, 3 H, CH3),3.63-5.00 (m, 7 H, OCH2CH20,OCH, OCH2CF3). IC was prepared analogously from 2-(2,2,2-trichloroethoxy)1,3,2-dioxaphospholane and pyruvic acid: 31PNMR (CDC13)6 -38.4, -38.8; 'H NMR (CDC13) 6 1.63 (d, J = 7 Hz, 3 H, CHJ, 3.95-5.00 (m, 7 H, OCH2CH20,OCH, OCH2CC13). Tri-n-butyl phosphate and di-n-butyl phosphate were obtained from Tokyo Kasei Co. (Tokyo, Japan) and used without further purification. Benzoyl chloride and methyl lactate were distilled before use. All solvents employed were reagent grade, dried by a conventional method, and distilled under nitrogen prior to use. Dinitrogen tetraoxide, obtained from Seitetsu Kagaku Co. (Osaka),was taken from a cylinder and dried over phosphorus pentaoxide before use. Measurement. NMR spectra were recorded on a Hitachi R-900 FT-NMR instrument operated at 36.4 MHz with wide-band proton decoupling. 31Pchemical shifts are given in parts per million from 85% HaPo4 external standard; positive chemical shifts are downfield from the standard. 'H NMR spectra were recorded on a Hitachi R-20B spectrometer with SiMe4 as an internal standard. IR spectra were obtained on a Hitachi 260-50 spectrophotometer. Molecular weight of the polymers was determined by vapor pressure osmometry in DMF at 55 OC on a Hitachi Perkin-Elmer Model 115 instrument. Gas chromatographic analyses were carried out on a Schimadzu GC-6A chromatograph. General Procedure of Polymerization. A typical procedure of hydrolysis polymerizations of la-c is as follows, where la is used as an example (entry no. 3 in Table I). To a stirred, 0 "C in 3 mL of acetonitrile solution of freshly prepared la (3.0"01) was added under nitrogen 59 mg of distilled water (3.3 "01) with a microsyringe. The mixture was gradually warmed to room temperature and allowed to stand for 5 days with stirring. During the reaction, a colorless paste was separated from the solution. After the polymerization, the paste was dissolved by adding 1mL of DMF, and the solution was poured into 70 mL of dry diethyl ether to precipitate the polymeric materials. The precipitated product was separated, and the supematant liquid was analyzed by GLC using trans-decalin as an internal standard to give the yield of phenol as 80% on the basis of reaction 1. The crude polymeric material was purified by repeated reprecipitation (twice from DMF solution to diethyl ether and once from trifluoroethanol solution to diethyl ether) to give 459 mg (78% yield) of the product
as a white powdery material. Treatment of Di-m -butyl Phosphate a n d Tri-n -butyl Phosphate with Benzoyl Chloride. To a stirred ice-cooled solution of 0.1 mL (0.5 mmol) of di-n-butyl phosphate in 1 mL of pyridine was added under nitrogen 0.2 mL (1.7 mmol) of benzoyl chloride. A part of the mixture was immediately placed into an NMR sample tube. Its 31P NMR spectrum showed quantitative formation of benzoyl phosphate 4 (6 -8.4). Treatment of tri-n-butyl phosphate with benzoyl chloride under similar reaction conditions caused no change in its 31PNMR signal at 6 -0.9 even after 1day at room temperature. Benzoylation of Polymer Samples for the 31PNMR Method. A polymer sample (ca. 0.1 g, 0.5 unit mmol) was dissolved in 0.5 mL of DMF. The solution was cooled to 0 O C with an ice bath, and to this were added 0.3 mL (4 mmol) of pyridine and of benzoyl chloride successively. A part of the 0.3 mL (2.6 "01) mixture was immediately placed into an NMR sample tube that had been dried and filled with nitrogen, and this sample was subjected to 31PNMR measurement. Polymer Salts of Triethylamine for the IR Method. First, an IR sample of the product polymer was obtained as follows. About 20 mg of the polymer was dissolved in 1 mL of methanol and a few drops of this solution was placed on a KBr plate. The solvent was evaporated, and the IR spectrum was recorded. Then, to the remaining methanol solution was added a sufficient amount of triethylamine. The second IR sample was prepared from the solution, and the spectrum was recorded. Triethylamine was added again to the remaining methanol solution, and the third IR spectrum was recorded concerning this mixture. The quantitative formation of the salts 6a and 6b was confirmed by comparing the second and the third IR measurement, no increase in strength of the band at 1600 cm-' being observed from the second to third measurement. Preparation of Model Compounds. Phenyl phosphate 9 was prepared previously." Cyclic phosphate 10 was obtained by two-step reactions as follows. Me c:>P-C,
I
t HOCHC02Me
EtsN
benzene
Me
I
15
Me
10 2-( 1-(Methoxycarbonyl)ethoxy)-1,3,2-dioxaphospholane (15).16 To an ice-cooled solution of methyl lactate (2.70 g, 25.9 "01) and triethylamine (2.61 g, 25.8 mmol) in 30 mL of benzene was added dropwise with stirring a solution of 2-chloro-1,3,2in 10 mL of benzene during dioxaphospholane" (3.22 g, 25.5 "01) 25 min. Stirring was continued at room temperature for an additional 50 min. The precipitate of the ammonium salt was removed by filtration, and the filtrate was concentrated to give a pale yellow oil, which was distilled to afford 3.73 g (75%) of 15 as a colorless liquid bp 63 OC (0.3 mmHg); 'H NMR (CDC13) 6 1.38 (d, J 7 Hz, 3 H, CH3), 3.61 (e, 3 H, CH,OCO), 3.73-4.23 = 7.1 Hz, &cop = 8.6 (m, 4 H, OCH&H20), 4.50 (two q, JHCCH Hz,1H, POCH); 31PNMR (CDCld 6 135.4; IR (neat) 1740 (M), 1450, 1210, 1120, 1010, 920, 880, 735 cm-'. Anal. Calcd for CcH11ObP: C, 37.12; H, 5.71; P, 15.96. Found C, 37.09; H, 5.51; P, 15.69. 2 4 l-(Methoxycarbonyl)ethoxy)-1,3,2-dioxaphospholane Into a solution of 15 (1.27 g, 6.53 mmol) in 15 2-Oxide mL of dichloromethane was introduced dinitrogen tetraoxide at -78 O C until the blue color of the oxidant did not disappear. The mixture was then kept at room temperature overnight. Concentration of the mixture and distillaton using a high-vacuum oil diffusion pump gave 1.00 g (73%) of 1 0 bp 57 "C (0.005mmHg); 'H NMR (CDC13) 6 1.58, 1.60 (two d, J = 7 Hz, 3 H, CH3), 3.80 (s,3 H, CH30CO), 4.15-4.80 (m, 4 H, OCH2CH20),5.00 (two q, JHCCH = 7 Hz, J H c o p = 8 Hz, 1 H, CHOP); 31PNMR (CDC13) 6 17.0; IR (neat) 1750 (C=O), 1450, 1280, 1220, 1100, 1030, 925,
Macromolecules 1984,17, 138-147
138
850 cm-’. Anal. Calcd for C6HII06P:c , 34.29; H, 5.28. Found C, 34.22; H, 5.39. Registry No. la, 61356-97-6; l b , 77989-23-2; IC, 77989-24-3; 10, 88229-79-2; 15, 88229-80-5.
References and Notes For a review, see: Kobayashi, S.; Saegusa, T. Pure Appl. Chem. 1981.53.1663. Saegusa, T.;Yokoyama, T.; Kobayashi, S. Macromolecules 1977. 10. 791. Kobayihi, S.; Hashimoto, T.; Saegusa, T. Macromolecules 1980,13, 1650. Kobayashi, S.; Yokoyama, T.; Saegusa, T. Polym. Bull. 1980, 3, 505. Kobayashi, S.; Chow, T. Y.; Saegusa, T. Macromolecules 1982, 15, 202. Kobayashi, S.; Huang, M. Y.; Saegusa, T. Polym. Bull. 1982, 6, 389. Saegusa, T.; Yokoyama, T.; Kobayashi, S. Polym. Bull. 1978, 1, 55. Saegusa, T.; Kimura, Y.; Ishikawa, N.; Kobayashi, S. Macromolecules 1976, 9, 724.
(9) Kobayashi, S.; Narukawa, Y.; Hashimoto, T.; Saegusa, T. Chem. Lett. 1980, 1599. (10) Kobayashi, S.; Narukawa, Y.; Shinkai, H.; Saegusa, T. Presented at the 47th Annual Meeting of the Chemical Society, Japan, 3135, 1983. (11) Kobayashi, S.; Narukawa, Y.; Mori, S.; Hashimoto, T.; Saegusa. T. Macromolecules 1983. 16.858. (12) (a) Lynen, F. Eer. Dtsch. Chem.’Ges. 1940, 73,367. (b) Cope, A. C.; Jackson, H. L. US. Patent 2 748 153,1956; Chem. Abstr. 1957,51, 498f. (13) Our preliminary results referred to the polymer structure as 2a.’ This was probably because the structure was examined with a polymer sample obtained after long reaction time. (14) (a) Khan, S. A.; Kirby, A. J. J. Chem. SOC. E 1970, 1172. (b) Cox, J. R., Jr.; Wall, R. E.; Westheimer, F. H. Chem. Ind. (London) 1959,929. (15) Saegusa, T.; Kobayashi, S.; Kimura, Y.; Yokoyama, T. J. Am. Chem. SOC. 1976,98, 7843. (16) Gerrard, W.; Richmond, M. J. J. Chem. SOC. 1945, 853. (17) Lucas, H. J.; Mitchell, F. W., Jr.; Scully, C. N. J. Am. Chem. SOC. 1950, 72, 5491. 1958,80, (18) Cox, J. R., Jr.; Westheimer, F. H. J. Am. Chem. SOC. 5441.
Conformational Study of the Dinucleotide dGpdCp-Tetrapeptide Ala4 Complex+ Young Kee Kang* and Mu Shik Jhon* Department of Chemistry, Korea Advanced Institute of Science and Technology, Seoul 131, South Korea. Received February 23,1983 ABSTRACT Conformational analysis of dinucleotide dGpdCp and tetrapeptide /3-alanine (Ala,),to the complex has been carried out with an empirical potential function by varying all the independent degrees of freedom of the nucleotide and peptide backbones. To understand the factors involved in the change of one conformation to another, we have estimated approximately the configurational entropies of the conformer and water molecules bound to it by using a potential surface analysis method. The total free energy changes for each conformational transition between dGpdCp, Al4, and their complex at room temperature were calculated and compared with each other. The free energy change of the free dGpdCp and Ala, to the free complex is -70.0 kcal/mol, in which the interaction energy change is -49.5 kcal/mol and the entropy change is 68.9 eu. Through the hydration, there have been large changes of free energies: -664.0 kcal/mol for dGpdCp, -72.0 kcal/mol for Ala,, and -682.3 kcal/mol for the complex. The entropy changes corresponding to them are -28.1, -48.3, and -178.5 eu, respectively. The free energy change of the hydrated dGpdCp and Al4 to the hydrated complex is -16.2 kcal/mol, in which the energy change is -26.1 kcal/mol and the entropy change is -33.2 eu. It is found that this entropy change is mainly caused by the conformational entropy change of dGpdCp and Ala, through the complex formation and that the major contribution to the total interaction energy is ascribed to the hydrogen bond between the conformer and water molecules bound to it, whereas the hydration effect of counterions and bound water molecules is proved to play an important role in determining the conformational stabilities of dGpdCp, Ala4, and their complex in the hydrated state.
I. Introduction The recognition between nucleic acids and proteins is one of the most fundamental processes and plays a central role in molecular communication in all living Examples of such interactions include complexes between histone and DNA, between repressor and DNA, between restriction endonuclease and DNA, and between transfer RNA and cognate synthetase. The “structural recognition” between nucleic acids and proteins can be classified into two categories: nonspecific interaction and specific interaction. In the former case, ‘From the thesis submitted by Young Kee Kang in fulfillment of the requirements for the degree of Doctor of Philosophy, Korea Advanced Institute of Science and Technology, Seoul, South Korea, 1983. *Presentaddress: Department of Chemistry, College of Natural Sciences, Chungbuk National University, Cheongju 310, South Korea.
protein recognizes some common structural features of nucleic acids and in the latter case, protein recognizes a particular base sequence of nucleic acids. Although ample experimental results- and model approa~hesl+’~ are available for these interactions, we know very little about the detailed mechanism of such interactions at the atomic or structural level. Carter and KrautlO proposed a model for a double-stranded RNA (ds RNA) and an antiparallel two-stranded @-sheet(@-ribbon),in which the 2’-hydroxyl of the ribose in RNA forms a hydrogen bond to the free carbonyl oxygen of the peptide backbone and the free NH group forms two hydrogen bonds through a water molecule with the ring oxygen and the 2’-hydroxyl oxygen of the next nucleotide on the narrow groove of ds RNA. They also pointed out that there is no room in the antiparallel @-ribbonfor residues other than those with very small side-chain groups since the narrow groove of ds RNA is too shallow and ruled out the possibility of a simiiar model for ds DNA because DNA lacks a 2’-hydroxyl group and
0024-9297/84/2217-0138$01.50/0 0 1984 American Chemical Society
